The present invention relates to a golf ball, more particularly to an improved dimple arrangement being capable of improving the aerodynamic symmetry.
The golf balls are provided with dimples on the spherical surface thereof. The dimples can promote eddy flow of the air during flying, which improve air resistance. Further, when backspin is given to the golf ball, the transition point from laminer air flow to eddy flow is differed between the upside and downside of the golf ball, and the dimples can increase the positional difference thereof, which improve lift.
Thus, it can be said that dimples are aerodynamically better if the laminer air flow along the golf ball surface is more disturbed thereby, and that wherever the rotational axis of backspin occurs on the golf ball, flight characteristics such as ballistic course height, flight duration, flying distance and the like should be invariable.
On the other hand, the golf balls are usually made with a mold, and it is difficult to form dimples on the mold parting line. Therefore, a golf ball has generally at least one parting line (corresponding to the mold parting line) on which dimples are not arranged.
If a backspin is given as shown in FIG. 11A wherein the circumferential speed of the golf ball is maximum along the parting line N (hereinafter such a hitting is called xe2x80x9cseam hittingxe2x80x9d), as the dimples are not arranged on the parting line N and thus the dimples effect is less, the ballistic course height and flying distance becomes decreased in comparison with a case of FIG. 11B wherein the rotational axis of backspin is on a plane including the parting line N (hereinafter such a hitting is called xe2x80x9cpole hittingxe2x80x9d).
It is therefore, an object of the present invention to provide a golf ball of which aerodynamic symmetry is improved to decrease flight characteristic variations depending on hitting position.
According to the present invention, a golf ball has
a spherical surface provided with a plurality of dimples,
a parting line extending on a great circle without crossing any of the dimples, and
a first great circle, a second great circle and a third great circle dividing the spherical surface into eight spherical equilateral triangles, wherein
the parting line crosses six of the eight spherical equilateral triangles, and
with respect to each of the first to third great circles, the number of dimples on one side of the great circle is equal to the number of dimples on the other side of the great circle.